In a device to device (D2D) communication scenario, in addition to accessing a network using a network side device (such as a base station), UE may access the network using another UE. In this process, UE that provides a network access function for another UE is a first device, such as a smartphone or another high-capability device, and UE that accesses the network using the first device is a second device, such as a wearable device (WD) or another low-capability device.
The first device accesses the network in two manners, contention-based random access and non-contention based random access. When the contention-based random access manner is used, the first device first sends a random access channel (RACH) preamble (PRACH) to a base station to notify the base station of a random access request such that the base station estimates a transmission delay between the base station and the first device and correspondingly calibrates uplink timing. Then, the base station sends a random access response (RAR) to the first device. Then, the first device sends information 3 (or message 3 (Msg 3)) to the base station. Finally, the base station sends a contention resolution message to the first device, and the first device accesses the network. When the non-contention based random access manner is used, the last two steps do not need to be performed.
Generally, each first device may connect to a plurality of second devices, and act as a relay to connect the second devices and the network. When the second device needs to upload data to the network, for example, the second device is a WD, and collected health data such as a blood pressure or a heart rate needs to be uploaded to the network, the second device needs to access the first device for data uploading. In addition, when the first device or the network side device pages the second device, and the second device listens and detects paging, the second device needs to access the first device to receive data. Currently, the second device accesses the first device in a manner in which the first device accesses the base station, that is, the contention-based random access manner and the non-contention based random access manner.
However, the second device is a low-capability device, and the random access process is relatively complex. If the second device accesses the first device in the random access manner, power consumption is high, consequently, a working time of the second device is short, and performance of the second device is severely affected.